New Zealand played with a high intensity in the first half in Lithuania and shut down the dangerous Slovenians, who were led by Phoenix Suns guard Goran Dragic.
But too many turnovers in the second spell allowed the Slovenians some offensive wriggle room and the New Zealanders struggled for rhythm as they blew a 37-27 halftime lead.
Tall Blacks coach Nenad Vucinic was left to rue how often his side gave the ball away.
"Our defensive intensity dropped in the second half, conceding 30 points in the last quarter which is disappointing.
''Defensively we allowed them some easy transitions, most of them coming from our turnovers. Again they were too high, we had 24 turnovers to nine, this type of statistic will make it hard to win any game."
Vucinic, who is still yet to decide on his final 12 players for the World Cup, which gets underway in two weeks, took the chance to rotate his squad against Slovenia.
The Tall Blacks play Lithuania at 4am tomorrow morning (NZT).
